Compressor apparatus



Sept. 26, 1944.`

Original Filed March 28, 1936 A. LYSHOLM COMPRESSOR APPARATUS 3Sheets-Sheet 1 Sept 26 1944- A. LYsHoLM COMPRESSOR APPARATUS QrignalFiled March 28, 1936 3 Sheets-Sheet 2 NVNI'R.

Sept. 26, 1944. AI LYSHOLM 2,358,815

COMPRES SOR APPARATUS Original Filed March 28, 1956 5 Sheets-Sheet 3 narl;- BY

NEY

Patented Sept. 26, 1944YY COMPRESSOR APPARATUS Alf Lysholm, Stockhohn,Sweden, assigner, by

to Jarvis C. Marble, Leslie M. Merrill, and APercy H. Batten, astrustees Application March 28, 1936, Serial No. 71,363. Renewed February8, 1940. In Sweden March 24 Claims. (Cl. 23d-143) The present inventionrelates to compressor apparatus and has particular reference to rotarycompressor apparatus of the lcrewor worm type. Still more particularlythe invention relates to compressor apparatus ior operation at constantor relatively constant speed and variable load, particularly asincorporated in gas turbine systems of the continuous combustion type.

Because of l the particularlyv advantageous utility in continuouscombustion gas turbine systems of compressor apparatus embodying theprinciples of the present invention, the invention will be consideredand .apparatus embOdying it will be described, in connection with gasturbine systems of the above mentioned type, but it is to be understoodthat the invention is not limited in its use to compressor apparatusembodied in this type of system.

In the case of a gas turbine plant where the compressor is driven by aturbine which is mechanically independent of the turbine producing powerforexternal use, the compressor capacity may be controlled within widelimits by changing the speed of operation of the compressorindependently of the speed of operation of the useful power turbine, thelatter, particularly in cases where it is employed to drive an electricgenerator, being usually operated at constant speed. This kind ofcompressor control is however not possible if the compressor is drivenby or mechanically connected to the useful power turbine and if theuseful power turbine can not be operated at variable speed because ofthe character of the power output therefrom. In the latter instance, thequantity of air delivered by the compressor can be controlled bythrottling to compensate for varying loads. 'I'his kind of control ishowever undesirable because it introduces into the system unavoidablethrottling losses. It has also been proposed heretofore to admit suctionair to diirerent stages of rotary compressors in a manner such that thesuction air is admitted to a pressure stage higher than the normal lowpressure stage when the load on the plant, and consequently the requiredoutput from the compressor, is reduced. With this method also, theemciency of the compressor drops materially from its normal efficiencywhen the compressor is operated under loads materially different fromthe normal load for which the compressor is designed. Control of the'compressor apparatus in order to take care of variable loads has alsobeen suggested, in which the work of compression is divided up among anumber ofindependently operable compressors, one or more of which may bedisconnected, depending upon the amount of change in the load imposed onthe system. This last-mentioned method of control is effective only to acertain extent, since by changing the number of compressors in operationit is possible to enect only a very coarse control of the quantity orpressure of the air delivered and in order to obtain the requisitenicety of control, resort must be had in addition to throttling, whichinvolves the introduction of the undesirable and unavoidable throttlinglosses.

Amongst the major objects of the present invention are: to provideimproved compressor apparatus capable of operating with acceptableefciency over a wide load rage while at the same time oper-)ating atconstant speed or with variations in speed which Vare relatively minoras compared with the degree of variation of the load; to provideimproved compressor apparatus of the screw type in which variable outputmay be obtained at constant speed of operation without involving unduelosses; to provide improved screw compressor apparatus in whichvariations in capacity ol.' the apparatus are obtained at con-i stantspeed by means of novel bleeding arrangements which permit a desiredquantity of air to be bled from the compression spaces of the compressorbefore compression commences; and to provide improved gas turbine systemapparatus of the continuous combustion type embodying compressorapparatus and controls therefore enabling the system to be Operatedeiliciently at variable load and with constant or substantially constantspeed of operation of the compressor apparatus constituting a part ofthe system.

For a better understanding of the nature of the present invention andthe advantages to be derived from its use, reference may best be had tothe ensuing portion of this specification in which is described severalembodiments of apparatus for carrying the invention into effect and tothe accompanying drawings forming a part hereof, in which suchembodiments are illustrated.

In the drawings:

Fig. 1 shows more or less diagrammatically in longitudinal cross sectiona gas turbine system of the continuous combustion type comprisingapparatus embodying the invention;

Fig. 2 is a section similar to Fig. 1 showing another arrangement ofapparatus embodying the invention;

lIl'ig. 3 is a wtransverse section through compresser apparatus havinghand operated bleeding means embodying the invention;

Fig. 4-is a longitudinal section partly in elevation of another form ofcompressor apparatus embodying the invention;

Fig. 5 is a section taken on the line 5-6 Fig. 4;

Fig. 6 is a plan view of the compressor shown in Fig. 4;

Fig. 7 is a view similar to Fig. 6 but with a portion of the compressorcasing broken away; and

Fig. 8 is a fragmentary section similar to Fig. 5 of a modification ofthe compressor apparatus shown in Figs. 4 to 7.

Referring now more particularly to Fig. 1, I0 designates generally adouble rotation radial flow gas turbine of known kind having shafts I2and I4 upon which are mounted the armatures of electric generators I6and I8. The turbine and generators are mounted in a common frame orcasing 28 having bearings 22, 24, 26 and 28. Shaft I2 is arranged todrive a compressor 30 and shaft I4 drives a compressor 32.

Compressor 30 is of the screw-type and, in the embodiment illustrated,comprises two rotors 34 and 38 mounted in suitable bearings in housing38. As will be observed from Fig. 1 and more particularly from Figs. 3,5,. and 8, a characteristic feature of the rotors is that they aredissimilar in cross-sectional contour, consisting of a male rotor havinglobes projecting wholly or substantially wholly beyond the pitch circleof the rotor, and a female rotor having grooves lying wholly orsubstantially wholly within the pitch circle of the rotor. Thisconstruction produces Working spaces having materially differentcharacteristics from those obtainable with intermeshing rotors of twinform such as are provided by intermeshing gears or rotors of the Rootstype and as employed in the appended claims, it, will be understood thatthe terms male rotor and female rotor define rotors of this dissimilarcross-sectional nature.

The rotors are preferably space packed. That is, clearance is providedbetween the rotors and the walls of the casing andgbetween theintermeshing portions of the rotors. The rotor construction mayadvantageously be in accordance with the principles disclosed in myco-pending application, Serial No. 44,935, filed October 14, 1935.Because of the utilization of space packing, the rotors may be operatedat the very high speed resulting from direct connection of the rotors tothe turbine. This connection is made through the coupling 48 connectingshaft I2 with the shaft part 42 of rotor/ 34. The gear 44, fixed on therotor shaft 42 meshes with gear 46 fixed to the shaft part 48 of therotor 38 and provides drive for the latter rotor and maintains theperipherally spaced relation of the intermesh- A ing parts of the tworotors. y Rotor 36 is provided side of the compressor as distinguishedfrom the suction side located behind the plane of the assaeis drawings.In order to prevent direct communication between the'inlet and theoutlet of the compressor, the end surfaces at the right of the rotorsare partly closed by an end wall member 48 which on its front side isprovided with an opening 8| for the flow therethrough of the com- 'inderfor a valve member such as the plunger 38 which when it is in theposition indicated in the ligure closes the opening 58. An annular space82 communicating with an outlet 84 provides communication between theinterior of the compressor casing and the atmosphere when. the valvemember 60 moves outwardly beyond the space 62. It will thus be evidentthat the opening afforded at 84, which may conveniently be termed ableeder-opening, may be brought into full or partial communication withthe interior of the compressor, depending upon the position of the valvemember 30.

The compression spaces formed in the compressor will be in communicationwith the bleeder opening at the moment when normal compression in suchspaces commences and if the bleeder valve is opened, compression in suchspaces will commence only after the time when the thread or lobelimiting the posterior boundary of the compression space has passed thebleeder opening. 'I'his will be at a time subsequent to the normalcommencement, of compression with the bleeder valve closed.

As indicated in the drawings, it is advantageous to have the bleedervalve extend, in its closed position, inwardly so that the inner end ofthe valve is flush with the inner surface of the casing and preferablythe inner face of the valve is made to conform to the curvature of thecasing. The reason for this is to avoid any large leakage space at thispoint, through which the air being compressed in one compression spacemay leak past the posterior limiting lobe, to the next succeeding spaceon the other side of such lobe.

The bleeder valve member 38 is provided with a stem 66 forming thearmature of a solenoid 68 and is also encircled by a spring 'I0 locatedbetween the housing-and an abutment plate 12. Spring i8 tends to movethe valve member to open position and this tendency is opposed by theaction of the solenoid winding, which when finally energized hassuflicient strength to overcome the action of the spring and maintainthe valve member in the closed position shown in the drawings. Solenoid68 is energized by current supplied through wires 'I4 and I6 from thegenerator mains indicated generally at I8.

The outlet 56 of the compressor 36 is connected by means of conduit to acombustion chamber 82 having a combustion space 64 surrounded by ajacket 86. Fuel such for example as oil is supplied by a pump, such asthat indicated at 88, to the burner nozzles indicated at and 32. Agovernor 94 operated from the shaft I4 actuates a fuel control member 96to control the amount of fuel fed to the combustion chamber underdierent conditions of load. A pressure relief valve Si connected to thedischarge pipe of the pump 88 permits return of fuel oil to the supplypipe of the pump through the return pipe 33 when the control member 96throttles or closes the passage of flow. The fuel control apparatus perse forms no part of the present invention and is diagrammaticallyillustrated. Any suitable apparatus for controlling the amount of fuelin y ""ase'is response` yto variationsy loadgon the system may beemployed. l

The .compressor` 32, whichV is yshown with its f suctionsidein frontofthe plane of the drawings, isr connectedby means of coupling 88 toshaft |4 and -ls similar in` construction to the compressor 30previouslyy described and need not be described in detail.` Compressor32 has air inlet openings vat and |02 and is provided with-ableeder'valve |04 urged toward openrposition by spring |08 and closedkby the solenoid |08, the latter being energized by currentderived`throughwires ||0 and i| 2 connected'into the electrical system'18.Theoutlet ||4 of compressor 32, which isplaced in communication with thecompression ,spaces of the compressor, by means ofthe port I |3'whichlies behind the plane of the paper, is connected by means of conduit ||8to the combustion Acharnberil2.v

Insofar as air iiow is concerned, it will be seen that compressors30-and 32 are arranged in parallel, both delivering to the outer chamberof the combustion apparatus, part of the air entering the inner chamberA84 to supply the oxygen necessary for. ,combustiony yof the fuel andthrough thejacket space around the ber. Motive fluid consisting of thegases from the inner chamber and inner chamcombustion the jacketing airisconducted through the 'twin pipes Hfandy the turbine I0 forexpansionin the turbine. Y s i As indicated, the generators `I8 and i8 feed intoa common electrical systemV and, as is usual in cases of thiskind,.operate synchronously.

With normal load on the system, the requisite yquantity of fuel ispumped to the combustion lchamber rand with the motive fluid generatedtherein by combustion of the fuel with the rair compressed in thecompressors, the turbine gencrates the power required to operate thegenerators and also the power required to in addition drive thecompressors.v Under such normal load conditionsgthe bleeder valves 'ofthe two compressors are closed Vand the compressors loperate under whatmaybe termedfull load compression.

When the load on, theplantchanges. the fuel supply is governed so thatan increased quantity of fuel is supplied Vupon increased'load and areduced quantity of` fuelis supplied with `decreasing load.,f',jAssumingconstant normal full load, the quantity of air delivered bythecompressor remains constant. Upon rdecrease in load, the closl ing eiectexerted by the,solenoids Iwhich hold the bleeder valves closed isdecreasedandthese valves,

will open to an extent governed by the degree o1' the reduction ,in theload,vso asjto openmore or lessthejbieeder openings.` Consequently, the

greater the decrease `infioad .on the plant, the greater will 'beg/th?quantity of air lwhich isgciisv chargedjthroughjtherbleederjiopeningsand the smaller will,"bejthelvjquantityjoffa'ir which" is com-".pr'essedintheicmpressrsjto ,the final pressure for delivery'gto.-the.-covrnbl'is'tion'ichamber; When the bleeder valves` are opened',the -nal pressure, vof the compressed airasjweuas the` y'qrnntity of'air `cornpressedfp'er unitofjtimew'ill be reduced,

because the ratio of vthe' volumeA oftherv compression spaces at thecommencement ofl ythe com V"pression perio'df to the volume thereof atthe end- [of the' compressionperiod constant. Il, aconstalnt finalpressure is desired regardless of varia.- "tions" in: "load'for, if the'final pressure'. is desired to beA variediwithj'.variations in load inla. manner other thanjthat ,e'il'ected` withthisapparatus;

this may beaccomplished by means to be herepart y owing inafterdescribed and adapted to vary the ratio of compression space volume atthe commencement and end of the compression periods.

The bleeder valve control need not necessarily be made dependent uponthe electrical load on the plant but may be controlled by any othersuitable factor which changes with and is indicative of changes in thevalue of the load.

An example oi such other control is illustrated in the plant shown inFig. 2. In this embodiment, ythe gas turbine |0a is indicated as beingof the axial ilow type connected for direct drive of a generator |22which delivers the power output of the system. Turbine 10a also drivesdirectly a compressor |24 similar in type to the compressors previouslydescribed except for the omission of the bleeder valve arrangement shownonl the compressor illustrated in Fig. 1. Compressor |24 is a highpressure compressor and is connected by means of a hydraulic coupling|28 of known construction to a low pressure compressor |28 which isalsooi the same screw type as that previously described. Bothcompressors are viewed from the presure side. Compressor |28 draws inlow pressure air through inlet openings |30 and |32 and has an outlet|34 connected by means of conduit |38 to the inlet |38 of compressor|24. The latter has an outlet |40 connected by conduit |42 to acombustion chamber 82 similar in construction to that described inconnection with Fig. 1. A governed fuel supply from pump 88 is suppliedto the burner nozzles 90 and 82 as previously described. Motive fluidformed in the combustion chamber from the fuel which is burned with theair supplied from the compressors is expanded in the turbine to producethe power required for driving the generator and the compressors. y

The 10W pressure compressor |28 is provided with an opening 84 and ableeder valve 60 controlling this opening, the construction beingsimilar to that previously described with reference to Fig. 1.` In thisinstance however, the control of the bleeder valve is different fromthat previously described. In this embodiment the stem 88 of the bleedervalve is provided with a piston |35 working with a. tight t in cylinder|31 and acted on by a spring 10 tending to move the piston and bleedervalve to a position in which the bleeder passage is opened. Theupperside of piston |35 is placed in communication with the compressedair conduit |42 by means of the pipe |44.

The hydraulic coupling |28 is placed in communication with a governorindicatedgeneraliy at |48 by means of a pipe |48. The governor comprisestwo plungers |50 and |52 connected to each otherand working in acylinder |54. A piston |58 is rigidly connected to the plungers |50 and|52 and works in a cylinder |58. A spring l 60 acts on one side ofpiston |58 while the other side of the piston is exposed to the pressureexisting in conduit |42 and pipe |44 by means of the connection |82.Pipes |84 and |66 connect the interior of the governor with a, liquidsupply `vessel |88. The vessel |88 is located-at a lower level than thatof the hydraulic couplingusothat the Working liquid may under certainconditions of operation flow by gravity from the coupling to the 'supplyvessel.` A gear pump |10 is located in .valve |14, on the discharge sideof pump,|10, permits return of working liquid from the pump to when thedischarge end oi pipe |86 is cltsed-eA by the governor.

Operation oi the system is as follows. Under full load operatingconditions, the bleeder valve 60 is closed, as shown in the drawings,the strength of spring '|0 being such that the spring is compressed byapplication of normal full load air pressure to the upper side oi piston|36. Governor |46, under the assumed full load condition, is as shown inthe drawings, with the pipes |64 and |48 connected and with` the inletend of pipe |66 closed. The working chamber of the hydraulic coupling isfilled with working iiuid and the two compressors are connected so thatboth are operated by the turbine. If it is now assumed that the load onthe generator is reduced, the fuel supply is correspondingly reducedthrough the action of the governor and associated control mechanism.This results in a. reduction of the temperature of the motive uid assupplied to the turbine because of the 'proportionately lower amount offuel as compared with air supplied to the combustion chamber. Thereduced temperature of the motive iluid results in a reduction in thepressure prevailing in the combustion chamber and in the pipe |42communicating therewith. This will be easily understood from thefollowing calculation. The quantity of motive iluid flowing through aturbine can be expressed by the equation:

F: KN/i P K- F VBT At the rst moments after reduction of the fuelsupply, the amount of motive fluid flowing` through the turbine isapproximately the same as before, the reduction in quantity dueto thedecreased fuel supply being of negligible order as compared with thequantity of air delivered by the compressor. Thus, if P and T representinitial pressure and initial temperature respectively at normal load,and P1 and T1 represent initial pressure and initial temperaturerespectively shortly upon reduction of the fuel supply,

For instance, if at normal full loa'd P=80 pounds per square inch,T=l800 degrees F. absolute,

"and if the temperature due to the reduced fuel supply is decreased toT1=1600, the pressure in the combustion chamber and in the pipe |42 willimmediately be reduced to P1=8 %3=75.4 pounds per square inch Due tothis reduction in the pressure the bleeder valve 60 commences toopenlunder the inuence f spring 10. 'Ihis openlng'or partial opening ofleialeeder valve 60 permits air to flow to a greater or lesser extentthrough the bleeder opening 64 to atmosphere. Thus, a reduced quantityot air, corresponding to the reduced load and the reduced fuel supply,will be compressed and supplied to the combustion chamber. Reduction ofthe quantity of air compressed will tend to bring the temperature of themotive fluid back to about normal value, the quantity of motive iluidproducedper unit of time now being reduced as compared with full loadconditions and the pressure of the motive iiuid being reduced alsobecause of the reduced pressure at which the air is ilnally deliveredfrom the compressor system because of the bleeding of some of the air.It will be seen that for every value of part load, there is a deilniteposition of the bleeder valve 60 and consequently for each suchvalue ofpart load, there is a deiinite quantity of air discharged from thebleeder opening. e

As the load on the system falls below the normal load value and as aconsequence the pressure in conduit |42 is reduced, the pressure actingon piston |56 of the governor will also .be reduced. This piston thencommences to move toward the right, as viewed in the figure, under theinfluence of spring |60 and this movement is transmitted to the plungers|50 and |62. Initial movement to the right from the position shown inthe gure will have no eilect on the hydraulic coupling but after theload and the pressure of the motive iluid have fallen below apredetermined value of part load, for example, idling 10aa, the plunger|50 wu close the outlet of pipe |64, and simultaneously the plunger |62will open the inlet of pipe |66. Movement of the governor to this.position closes the connection between pump |10 and the coupling, whichis instead connected through pipes |48 and |66 to the supply vessel |68to which the working uid in the coupling will ow by gravity, in thedirection indicated by the arrow |18. Draining of the working fluidfrom`v the hydraulic coupling renders this coupling inoperative and thevcompressor |28 ceases to operate. At this time a spring loaded checkvalve in the air conduit |36 connecting the two compressors is opened bythe suction created by the compressor |24 and air is now compressed onlyin this compressor.

I f the load increases from the value at which compressor |28 isrendered inoperative, the accompanying increase in the amount of fuelsupsure of the motive iiuid. 'I'he increased pressure of the motive nuidacting on piston |56 of the governor moves the plunger valves of thelatter to the left and when a predetermined value of load is reached,the original connections are established, that is, the pump is againconnected with the hydraulic coupling and the drain pipe |68 is closed.The pump rells the coupling with working liquid and the low pressurecompressor |28 is brought back into operation. Reestablished operationof the low pressure compressor produces pressure in the connectingconduit |38 and as a consequence valve |80 closes. With this valveclosed, the compressors again operate in series. Further increase inload causes the bleeder valve 60 to be brought more and more nearly t'oclosed position, progressively cutting down theamount of air bled fromthe low presmeand,whennonnalfuliloadha|liconreaelied,thepartslieasainintimpositicm f in yWhile automaticcontrol of the bleeder valve or Valves is advantageously employed,manual control face of which is curved to form a continuation ofthecylindrical inner surface of the casing. A

'space vi|| surrounding the valvecommunicates with the bleeder outletpassage 2||. A stem 2|2 is attachedto the valve and is provided with akey 2|2a working in a suitable slot in the yoke 2|| to prevent rotationoi' the bleeder valve. The vupper portion of the stem is threaded at 2|4through the hub of a hand wheel 2||, the rotation of which on thethreaded stem acts to lift the valve.

In the position of the apparatus shown. the bleeder valve is closed andcompression of trapped air takes place inthe compression space 2I|between the threads or lobes 2I2 and 2 i4 of the rotor |22. Space 2 i|extends helically toward the suction side of the compressor to a pointwhere a cooperating thread or lobe of the rotor i|4 projects into thespace so as to progressively reduce its volume upon rotation of therotors in the directions indicated. The succeeding compression space2I4, looking in the direction of rotation of the rotor. is still incommunication with the suction side and remains so until the edge 2I| ofthe lobe 2li reaches the left hand unitingedge nl of the bleederopening. At this moment. compression commences in space 2I|. If thebleeder valve l|| is then opened, air may escape through the bleederopening without its having been appreciably compressed. From theforegoing it follows that. for instancespace 2| is in communication withthe bleeder valve i|| during the period from the instant the edge 2i| ofthe lobe 2I4 reaches the left hand limiting edge 22| of the bleederopening to the instant the edge 2 of the lobe 2I2 reaches the. righthand limiting edge 222 of the bleeder opening.

Advantageously the bleeder opening ||2 is shaped so that communicationof the compression space with the atmosphere takes place with minimumthrottling losses. To this end, it is preferable to make the limitingedges 22| and 222 of the bleeder opening parallel, or approximatelyparallel. to the helical edge 2i| of lobe 2|2 and consequently in thesame relation with respect to the corresponding edges of the remaininglobes of the rotor. With the limiting edges of the bleeder openingparallel to the outer edges of the rotor lobes, maximum speed of openingand closing of the bleeder opening with respect to the compressionspaces, will be obtained.

By making the lower surface of the bleeder valve curved to conform tothe curvature of the inner surface of the casing, leakage back from thecompression space 2in to the space 2i| is prevented when the edge 2I|passes the bleeder 5 opening I|2 under full load operating conditionsclosed.

vwhen the bleeder valve is As previously mentioned, the relation ofthevariation in final compression pressure to the variation in the quantityof air compressed at part loads can be varied as desired by changing thecompression ratio which is eected under different conditions of 10nd.

Apparatus for accomplishing this is shown in Figs. 4 to '1. Referringnow to these comprises a casing 224 in which rotors 22| and 22| aremounted, these rotors being geared together as in the compressorspreviously described and being adapted to be driven by means of a powerinput shaft 220. In this embodiment, six lobes are shown on one rotorand seven on the other in contrast to the three lobes shown for examplein Fig. 3. It will be understood that the number of lobes per rotor maybe varied as desired within the scope of the present invention.

The casing 224 is provided with inlet openings 22| and 221 and an outlet229. In this instance, it will be observed that the inlet ports in thecasing provide for both radial and axial admission of air to thecompression spaces and both radial and axial discharge from thecompression spaces.

Casing 224 has a portion 232 which does not follow the contour of therotors but is spaced therefrom and in the space provided between therotors and this portion of the casing, a slide 234 is provided, theinner surface of which is formed to the same radius as the radii of therotors. This slide is axially movable as indicated in Fig. 4, throughthe medium of a control rod 23| which may be either manually operated oroperated gures, the compressor 'automatically in response to loadvariations on curved edges 24| and 248, these latter edges determiningthe area for radial exhaust from the compression spaces and consequentlyaffecting the total Vexhaust area from these spaces and the dischargepressure of the compressed air.

If we now assume the slide to be moved to the extreme right handposition with edges 238 and 24| abutting respectively against edges 242and 244, compression will commence at the moment intended for normalfull load compression. This will be at the time when the edges of therotor lobes, which cooperate to form a given compression space, pass thelimiting edges of the inlet ports.

If it is desired to decrease the quantity of air delivered by thecompressor. the control member or slide 224 is moved to the left fromits extreme right hand position, to a position such for example as thatshown in Fig. 'I and this movement opens up passages 254 and 256 betweenthe end edges 22| and 240 of the slide and the respectively cooperatingcasing edges 242 and 244. It will be evident that with the slide movedto this position, commencement of compression in any given compressionspace will be delayed until the edges of the lobes deilning theposterior boundary of suchspace pass beneath the slide edges 238 and240.

If for the moment we disregard the eiiect on the outlet opening or themovement of the slide to the left from its full load position.- it willbe evident thatthe compression ratio will be altered by such movement tothe left since the volume of the compression space at the moment com-lpression commences is decreased as compared with full load adjustment.while the volume of the compression space at the moment when the exhaustport opens remains constant. This terior boundary of the compressionspace has would result in decreased pressure at the moment of dischargefrom the compressor space.

Obviously however, movement of the control slide toward the left to apart load position will cause the area of the outlet opening to bedecreased and, consequently, as the volume of the compression space atthe instant compression commences is decreased by movement of the slide,the volume when exhaust occurs is de-' creased and the final compressionvolume is also decreased. It will be evident that the change in therelation of the volume of the compression space at the moment whencompression commences to the volume of the compression space at themoment when exhaust or discharge commences can be varied as desired bysuitably relating the contours of the edges of the slide which controlthe commencement of compression and the termination of compression inthe various positions of the slide.

From the foregoing description of this embodiment, it will be evidentthat the control slide constitutes a bleeder valve for delaying thenormal time of commencement of compression as compared with full loadcompression. By use of the slide form of bleeder valve, it is howeverpossible, if desired, to accomplish the additional function with thissingle valve member of obtaining such constancy or variation in thecompression ratio with change in compressor capacity as may be desired.

Fig. 8 shows a modiiication of the apparatus illustrated in Figs. 4 to7. The construction is similar to that described above except the formof the control member or slide which in this instance is in the form'ofa cylinder 250 the lower f portion of which is cut oi and connected witha member 262 the inner surface of which is formed to the same radius asthe radii of the rotors. As in the example previously described, thecontrol member is axially movable by means of a control rod 284. As willbe easily understood from the drawings, the shape of the control member260 facilitates manufacturing of the apparatus as compared with theshape of the control member according to Figs. 4 to 7.

From the foregoing description, it will be evident that many specificdifferent forms of structure may be employed .within the scope of theinvention and it is to be understood that the invention embraces allthat falls within the scope of the appended claims when they areconstrued as broadly as is consistent with the state of the prior art.

Certain subject matter disclosed but not claimed in this applicationforms the claimed subject matter of my copending application SerialNumber 500,010, filed August 25, 1943.

I claim:

1. A compressor of the rotary screw type including a casing having aninlet and an outlet for fluid and an end wall, a plurality of rotorsmounted in said casing, each of said rotors havpassed, said opening andmeans for controlling iiow through said opening.

2. A compressor' of the rotary screw type including a casing having aninlet and an outlet for fluid and an end wall, a plurality of rotors,mounted in said casing, each of said rotors having spiral lobes andintervening spiral grooves of uniform height and depth respectivelyalong their lengths, the lobes and groovesfintermeshing and cooperatingwith each other and with the casing to form spaces registering atdifferent times with said inlet and said outlet and which are displacedaxially of the compressor by rotation ot the rotors to come intocommunication with said end wall, a bleeder opening in said casinglocated so that compression can commence in any one of said spaces onlyafter the rotor lobe defining a pos-. terior boundary of the compressionspace hasl passed said opening, said opening having opening and closingedges disposed substantially parallel to the edges of the rotor lobespassing the opening and means for controlling iiow through said opening.

3. A compressor of the rotary screw type including a casing having aninlet and an outlet for uid and an end wall, a plurality of rotorsmounted in said casing, each of said rotors having spiral lobes andintervening spiral grooves of uniform height and depth respectivelyalong their lengths, the lobes and grooves intermeshing and cooperatingwith each other and with the casing to form spaces registering atdifferent times with said inlet and said outlet and which are displacedaxially of the compresor by rotation of the rotors to come intocommunication with said end Wall, a bleeder opening in said casing forpermitting escape from the compressor of fluid in said spaces, a valvefor controlling'said opening, said valve having a smooth inner surfacewinch in closed position of the valve provides substantially acontinuation of the inner surface of the casing and means for actuatingsaid valve to open or close said opening.

4. A compressor of the rotary screw type including a easing having aninlet and an outlet for fluid and an end wall, a plurality of rotorsmounted in said casing, each of said rotors having spiral lobes andintervening spiral grooves of uniform height and depth respectivelyalong their lengths, the lobes and grooves intermeshing and cooperatingwith each other and with the casing to form spaces registering atdiierent times with said inlet and said outletl and which are displacedaxially of the compressor by rotation of the rotors to come intocommunication with said end wall, and means movable relative to saidcasing to alter the volume of the spaces at the beginning of compressiontherein.

5. A compressor of the rotary screw type including a casing having aninlet and an outlet for fluid and an end wall, a plurality of rotorsmounted in said casing, each of said rotors having spiral lobes andintervening spiral grooves oi uniform height and depth respectivelyalong their lengths, the lobes and grooves intermeshing and cooperatingwith each other and with rotary screw type in-f cluding a casing havingan inlet and an outletf:l

for iluid and an end wall, a' plurality oi rotors mounted in saidcasing, each of said rotors having spiral lobes and intervening spiralgrooves` oi uniform height and depth respectively along;

their lengths, the lobes and grooves intermeshing and cooperating witheach other and with the casing to form spaces registering at differenttimes with said inlet and said outlet and which are displaced axially oithe compressor'by rotation of the rotors with said end wall and amounted between said casing and said rotors and cooperating with therotors and with portions of the casing to vary, upon movement of themember. the volumesof the spaces at the commencement of compression andthe volumes of the spaces at the termination of compression, thevariation in said volumes due to such movement oi the member eil'ectng achange in the compression ratio of the compressor. t

7. A compressor of the rotary screw type into come into communicationmember movably Amencement therein at fullload. i; l 9. yIn. theoperation ot l a rotary compressorof the: type-v havinga lcasingprovidingv an; inlet and.

ankoutlet:forr ilu id,,a 4 plurality of rotors mounted ,Y

speed.v oit- .koperation thereof; comprising5a bleeder valve membermovable tovent said spaces until their kplume is less'thanthevolumeatthefmoment oi commencement of vfull load compression, l

whereby to-delay thegcommencement of compressiony injsuchspaces ,ascompared with for rotation in said casinssmehrof said krotors AhavingIspiral lobes and intervening-spiral grooves,yv r of uniformi heightyand. Adepth respectively along l thelfylenths, the lobes and groovesintermeshl ing and cooperatingwitheach other and with the casing tolformspacesregisteringgatE ditlerent timeswith saidixiletandvsaid outletand'which arex displaced axially ,of the compressor upon rotation ofthe-rotors so asttocoxne into communication with an en d wall of .theAcasingl to eiIect compression, that improvement which consists invvarying thecapacityoi the compressor while maintainingsubstantiallyconstant speed of operation thereof by altering y,the`eilective initialvolume for compression of said spaces.

10. `In the operation of, a rotary *compressor of the typehaving aCasing providing kan inlet and e an outlet for iluid, apluralityofrotors mounted cluding a casing having an inlet and an outlet for lspiral grooves of for rotation insaidl casing, each of said rotorshaving spiral lobes and intervening spiral grooves of kuniform heightand depth respectively along their lengtha'the lobes and groovesintermeshing and 'cooperating lwith* eachother and with the casingtoiorm lspaces registering at Adifferent times with said' inlet andsaid` outlet and which are displaced axiallyfof the compressor upon yro-40 tation of the rotors so as tc come into communiand cooperating witheach other and with the casing to form spaces registering at diilerenttimes with said inlet and said outlet and which are displaced axially ofthe compressor` by rotation of the rotors to come into :communicationwith said end wall to compress and discharge uid adjacent said end wall,an axially slidable member interposed betweeny said rotors and a portionof said casing, said member having an end arranged to move awayiromcooperating portions of the casing to provide passage for n escape oi'fluid from the spaces upon movement of said member toward thedischargeend ofthe compressor, whereby to delay commencement o1'l the compressionperiod, and said member having an opposite end portion vfor reducing thearea kof the outlet opening of the compressor upon movement of themember toward the discharge end of the compressor, and means operablefrom the exterior of the compressor yfor adjusting lthe position of saidmember. v Y v v 8. A compressor of the rotary screw type including acasing having ,anl inlet and an outletv for fluid and an end wall, aplurality oi' rotorsv mounted in said casing, each of said rotors havingspiral lobes land intervening spiral groovesv of uniform heightanddepthrespectively along,

their lengths, the lobes and grooves intermeshing and cooperating .witheach othervand with the casing to iormyspacesfrregistering at dlilerenttimes with said inlet and said outlet and which are displacedariallyoithecompressorxby rotacation kwith an end wall of fthe casing to effectume by'decreasing the eiectviveiinal compression ,volume loi.' saidspaces.,

1l. A compresor of. the rotary screw `type including 4a casinghavingan'Ainlet and an 4outlet i'or iluld'and anv end Wall,l a plurality of,rotors mounted insaidcasing, each of said rotors having vspiral: lobesand intervening spiral lgrooves y of uniformheightand depthrespectivelyalong their lengths, the' lobes` `and grooves intermeshingandcooperating with each other and with the,

casingto'forml spaces registering at different times with saidinlet andvsaid outlet andwhich are vdisplaced axially, of the compressor byrotation'of lthe rotors` to come into communication with said'endwall,,and meansincluding a bleeder valve 'member 'adjustable to causeinitiation of partl loadycompression in any given compression 'space.'with said rotors v in any. different angular positions of rotation.

12. Acompressor of the rotary screwA type including acasinghavingnninletand an outlet for ijluid endwall,\a `plurality-ofrotors mounted in said casing-,.each of ,said -rotors haveingfspirallobes and intervening spiralgrooves f of uniformheightand-depth respectively alongk theirlengths, the lobeaand; groovesintermeshing: Y v

and `cooperating;witheach otherandwith the withV said endywall,`andfmeans ,fori varyingthe capacity ofthe compressor.A without'changinggthe ,thek com- 4.

oneof a seriesoi y.

casing to form spaces registering at different times with said inlet andsaid outlet and which tion of the rotors with respect to both theinitiation and the termination of compression in any given one of saidspaces.

` 13. A compressor of the rotary screw having a casing providing aninlet and an outlet for iiuid, a plurality of rotors moimted forrotation about parallel axes in said casing including a male rotor and afemale rotor having intermeshing spiral lobes and grooves respectively,the intermeshing lobes and grooves being of substantially uniform heightand depth respectively along their lengths and cooperating with eachother and with the casing to form compression spaces registering atdinerent times with said inlet and said outlet and being decreased involume by contraction in a direction parallel to the axes of said rotorsafter passing out of communication with said inlet and before cominginto communication with vsaid outlet, a bleeder opening in said casinglocated so that compression can commence in any v .one of said spacesonly after the rotor lobe dellning a posterior boundary of thecompression space has passed said opening and means for cona aboutparallel axes in said casing including a male rotor and a female rotorhaving intermeshing spiral lobes and grooves respectively, theinterstantially a continuation of the inner surface4 of Ythe casing andmeans forb actuating said valve to open or close said opening.

16. A compressor of the rotary screw type having a casing providing aninlet and an outlet for fluid, a plurality of rotors mounted forrotation about parallel axes in said casing including a male rotor and afemale rotor having intermeshing spiral lobes and grooves respectively,the intermeshing lobes and grooves being of substantially uniform heightand depth respectively along their lengths and cooperating with eachother and with the casing to form compression spaces registering atdifferent times with said inlet and said outlet and being decreased involume by contraction in a direction parallel to the axes of said rotorsafter passing out of communication with said inlet and before cominginto communication with said outlet, and means movable relative to saidcasing to alter the volume of the spaces at the beginning of compressiontherein.

17. A compressor of the rotary screw type having a casing providing aninlet and an outlet for iluid, a plurality of rotors mounted forrotation about parallel axes in said casing including a male rotor and afemale rotor having intermeshing spiral lobes and grooves respectively,the intermeshing lobes and grooves being of substantially uniform heightand depth respectively along their lengths and cooperating with eachother and with the casing to form compression spaces meshing lobes andgrooves being of substantially uniform height and depth respectivelyalong their lengths and cooperating with each other and with the casingto form compression spaces registering at different times with saidinlet and said outlet and being decreased in volume by contraction in adirection parallel to the axes of said rotors after passing out ofcommunication with said inlet and before coming into communication withsaid outlet, a bleeder opening in said casing located so thatcompression can commence in any one of said spaces only after the rotorlobe defining a posterior boundary of the compression space has passedsaid opening, said opening having opening and closing edges disposedsubstantially parallel to the edges of the rotor lobes passing theopening and means for controlling ow through said opentering atdifferent times with said inlet and said outlet and being decreased lnvolume by contraction in a direction parallel to the axes of said rotorsafter passing out of communication with said inlet and before cominginto communication with said outlet, a bleeder opening in said casingfor permitting escape from the compressor of Vduid in said spaces, avalve for controlling said opening, said valve having a smooth innersurface which in closed position of the valve provides subregistering atdifferent times with said inlet and said outlet and being decreased involume by contraction in a direction parallel to the axes of said rotorsafter passing out of communication with said inlet and before cominginto communication with said outlet, and means movable relative to saidcasing for altering the volume of the spaces at the commencement ofcompression therein and simultaneously altering the volume of thecompression spaces at the termination of compression therein.

18. A compressor of the rotary screw type having a casing providing aninlet and an outlet for uid, a plurality of rotors mounted for rotationabout parallel axes in said casing including a male rotor and a femalerotor having intermeshing spiral lobes and grooves respectively, theintermeshing lobes and grooves being of substantially uniform height anddepth respectively along their lengths and cooperating with each otherand with the casing to form compression spaces registering at differenttimes with said inlet and said outlet and being decreased in volume bycontraction in a direction parallel to the axes of said rotors.

after passing out of communication with said inlet and before cominginto communication with said outlet, and a member movably mountedbetween said casing and said rotors and cooperating with the rotors andwith portions of the casing to vary, upon movement of the member, thevolumes of the spaces at the commencement of compression and the'volumes of the spaces at the termination of compression, the variationin said volumes due to such movement of the member efv fecting a changein the compression ratio of the compressor.

lengths and cooperating with each other and with the casing to formcompression spaces registering at different timeswith said inlet andsaid outlet and being decreased in volume by contraction in a directionparallel to the axes of said rotors after passing out of communicationwith said inlet and before coming into communication with said outlet,an axially slidable member interposed between said rotors and a portionof said casing, said member having an end arranged to move away fromcooperating portions of the casing to provide passage' for escape offluid from the spaces upon movement of said member toward said outletwhereby to delay commencement of the compression period and said memberhaving an opposite end portion for reducing the area of the outletopening of the compressor upon movement of the member toward the outlet,and means operable from the exterior of the compressor for adjusting theposition of said member.

20. A compressor of the rotary screw type having a casing providing aninlet and an outlet for fluid, a plurality of rotors mounted forrotation about parallel axes in said casing including a male rotor and afemale rotor having intermeshing spiral lobes and groovesrespectively,`the interrneshing lobes and grooves being of substantiallyunifonn height and depth respectively along their length and cooperatingwith each other and with the casing to form compression spacesregistering at different times with said inlet and said outlet and beingdecreased in volume by contraction in a direction parallel to the axesof said rotors after passing out of communication with said inlet andbefore coming into communication with said outlet, and means for varyingthe capacity of the compressor without changing the speed of operationthereof comprising a bleeder valve member movable to vent said spacesuntil their volume is less than the volume at the moment of commencementof full load compression, whereby to delay the commencement ofcompression in such spaces as compared with the commencement therein atfull load.

21. In the operation of a rotary compressor of the type having a casingproviding an inlet and an outlet for fluid, a plurality of rotorsmounted for rotation about parallel axes in said casing including a malerotor and a female rotor having intermeshing spiral lobes and groovesrespectively, the intermeshing lobes and grooves being of substantiallyuniform height and depth respectively along their lengths andcooperating with each other and with the casing to form compressionspaces registering at diiTerent times with said inlet and said outletand being decreased in volume by contraction in a direction parallel tothe axes oi'A said rotor after passing out of communication with saidinlet and before coming into communication with said outlet to effectcompression, that improvement which consists in varying the capacity ofthe compressor while maintaining substantially constant speed ofoperation thereof by altering the eiIective initial volume forcompression of said spaces.

22. In the operation of a rotary compressor of the type having a casingproviding an inlet and an outlet for fluid, a plurality of rotorsmounted for rotation about parallel axes in said casing including a malerotor and a female rotor having intermeshing spiral lobes and groovesrespectively, the intermeshing lobes and grooves being of substantiallyuniform height and depth respectively along their lengths andcooperating with each other and with the casing to form compressionspaces registering at diierent times With said inlet and said outlet andbeing decreased in volume by contraction in a direction parallel to theaxes of said rotors after passing out of communication with said inletand before coming into communication with said outlet to effectcompression, that improvement which consists in reducing the capacity ofthe compressor while maintaining substantially constant speed ofoperation by decreasing the effective initial volume for compression ofsaid spaces, and modifying the decrease in delivery pressure which wouldresult from such decrease in effective initial volume by decreasing theeffective final compression volume of said spaces.

23. A compressor of the rotary screw type having a casing providing aninlet and an outlet for i'luid, a plurality of rotors mounted forrotation about parallel axes in said casing including a male rotor and afemale rotor having intermeshing spiral lobes and grooves respectively,the intermeshing lobes and grooves being of substantially uniform heightand depth respectively along their lengths and cooperating with eachother and with the casing to form compression spaces registering atdifferent times with said inlet and said outlet and being decreased involume by contraction in a direction parallel to the axes of said rotorsafter passing out of communication with said inlet and before cominginto communication with said outlet, and means including a bleeder valvemember adjustable to cause initiation of part load compression in anygiven compression space with said rotors in any one of a series ofdifferent angular positions of rotation.

24. A compressor of the rotary screw type having a casing providing aninlet and an outlet for fluid, a plurality of rotors mounted forrotation about parallel axes in said casing including a male rotor and afemale rotor having intermeshing spiral lobes and grooves respectively,the intermeshing lobes and grooves being of substantially uniform heightand depth respectively along their lengths and cooperating with eachother and with the casing to form compression spaces registering atdifferent times with said inlet and said outlet and being decreased involume by contraction in a direction parallel to the axes of said rotorsafter passing out of communication with said inlet and before cominginto communication with said outlet, and control means having adjustableportions cooperating with said rotors to vary the relation of theangular position of rotation of the rotors with respect to both theinitiation and the termination of compression in any given one of saidspaces.

ALF LYSHOLM.

